This invention relates to a novel apparatus for cooling a semiconductor die. More specifically, this invention relates to an apparatus for cooling an integrated-circuit chip by circulating a cooling liquid around the chip.
In the design of optimal computer systems, it is important that the most number of integrated circuit chips are fit into the least amount of space. Integrated circuit technology has advanced so that extremely small chips can be produced which have significantly more computing power than in previous years. Chip packaging design is also an important factor affecting the size of the computer circuitry. While there are a number of advantages to decreasing the size of semiconductor chips, associated problems have also arisen. For instance, as the chip size decreases, the heat emitted from the chip becomes problematic because it is difficult to cool such a small element. The chip packaging design also affects how efficiently the chip may be cooled. As the chip temperature increases, the effective operating speed of the chip decreases. Also, it is necessary to keep the chip below a certain temperature in order to prevent damage to the chip circuitry.
Semiconductor chips are often elements in complex systems which are built from a plurality of printed circuit boards, which are themselves interconnected by other printed circuit or mother boards. The resulting system is relatively bulky and yet compact. Since the systems are compact, effective cooling systems are needed to remove the heat which evolves during operation. Some cooling systems result in even bulkier packages which utilize valuable circuit board space.
In order to facilitate cooling, individual semiconductor chips and semiconductor chip systems have been designed to permit convection about and within them. The convection may be natural or forced, and air has been used as the cooling medium. Circulating air has helped to remove some of the heat emitted from a semiconductor chip, but it is oftentimes an undesirable means of doing so. Natural convection is not an efficient cooling method, and forced air convection has the disadvantage of polluting the circuits by rapidly covering them in dust.
Another method of cooling semiconductor chips is to circulate a liquid around a chip. A cooling liquid cools the chip more efficiently than air and obviates the problems associated with air convection. While the liquid cooling systems that have been developed are an improvement over air convection systems, a semiconductor die sometimes remains at an undesirable temperature because the circulating fluid cannot absorb enough heat to adequately cool the chip. More specifically, the fluid flow may not be evenly distributed around the chip. Additionally, temperature gradients may exist on the chip surface, thereby causing the chip to operate improperly.
Some prior art devices utilizing liquid for cooling have included complex structures which are difficult to fabricate. One type of arrangement, as shown in U.S. Pat. No. 4,547,834 to Dumont et al., includes a plurality of levels to support a semiconductor chip and permit cooling of the chip. Some of the levels are separated to form an opening through which the liquid circulates to cool the semiconductor die. A plurality of column supporters hold up a layer of metal under which the liquid circulates. This arrangement is unsatisfactory because it is complex, expensive, and somewhat difficult to fabricate.
Semiconductor chip cooling arrangements must additionally take into account the type of die packaging. For example, the die may be packaged utilizing a common packaging design called tape automated bonding (TAB). TAB, a replacement for wire bonding, utilizes a tape having leads fabricated on its surface. The tape is connected to the die so that the leads may be bonded to the appropriate die surfaces. TAB is a useful packaging method because it is simple and reliable.
Another cooling package is described in U.S. Pat. No. 4,748,495 to Kucharek, and includes a structure having a coolant path through a heat sink. The heat sink is adjacent to a heat spreader, which is adjacent to the top surface of an IC chip. Heat emitted from the IC chip is transferred to the heat sink via the heat spreader by means of a cooling liquid. The heat sink structure is somewhat complex and includes a plurality of parallel channels through which the liquid flows. Kucharek mentions that the structure may be adaptable for chips having tape automated bonded (TAB) contacts. While the package reduces the temperature of the IC chip more than air convection units, the complexity and accompanying cost of the unit are undesirable. Additionally, the package is bulky and takes up valuable circuit-board space. Other types of packaging arrangements include similarly complex designs which are expensive to fabricate.
The difficulties suggested in the preceding are not intended to be exhaustive, but rather are among many which may tend to reduce the usefulness of prior semiconductor chip cooling apparati. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that semiconductor chip cooling apparati in the past will admit to worthwhile improvement.
It is therefore a general object of the invention to provide a novel semiconductor chip cooling apparatus which will obviate or minimize difficulties of the type previously described.
It is a specific object of the invention to provide a semiconductor chip cooling apparatus which will efficiently cool a semiconductor chip.
It is another object of the invention to provide an apparatus for cooling a semiconductor chip which is packaged using tape automated bonding (TAB) techniques.
It is still another object of the invention to provide a semiconductor chip cooling apparatus which is compact.
It is yet another object of the invention to provide a semiconductor chip cooling apparatus which is relatively simple to manufacture, inexpensive, and reliable.